1. Field of the Invention
This invention relates to a radiation image read-out apparatus for use in a radiation image recording and reproducing system. This invention particularly relates to a radiation image read-out apparatus wherein a read-out section and an erasing section are combined integrally.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet or simply as a sheet) is first exposed to a radiation passing through an object to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, and the radiation image of the object is reproduced as a visible image by use of the image signal on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the aforesaid radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store a radiation image until the sheet is scanned with stimulating rays for reading out the radiation image. Therefore, after the radiation image is read out from the stimulable phosphor sheet, radiation energy remaining thereon should be erased to reuse the sheet.
For satisfying this requirement, it has been proposed to provide a radiation image read-out apparatus with a read-out section for reading out an image stored on a stimulable phosphor sheet, and an erasing section for erasing radiation energy remaining on the sheet.
In the proposed radiation image read-out apparatus, a cassette housing a stimulable phosphor sheet carrying a radiation image stored thereon by use of an external image recording apparatus is fed to a cassette holding section, and the stimulable phosphor sheet is taken out of the cassette and sent to the read-out section for reading out the radiation image. After the image read-out is finished, the sheet is sent to the erasing section where radiation energy remaining on the sheet is erased. The erased sheet is taken out of the read-out section and reused for image recording.
The aforesaid radiation image read-out apparatus is desired to be fabricated in a small size so that it can be used in a limited space. Accordingly, there have been proposed various read-out apparatuses whose sizes are made small by devising, for example, the layout of the read-out section, the erasing section or the like.
As for the radiation image read-out, there has heretofore been known a method wherein preliminary read-out for approximately ascertaining the radiation image stored on a stimulable phosphor sheet is conducted prior to the aforesaid image read-out (final read-out) for obtaining an electric image signal for use in reproduction of a visible image, image read-out conditions for the final read-out or the like are adjusted based on the information obtained by the preliminary read-out, and the final read-out is carried out by use of the adjusted read-out conditions.
As disclosed, for example, in Japanese Unexamined Patent Publication No. 58(1983)-67240, the preliminary readout may be conducted by scanning the stimulable phosphor sheet with stimulating rays having stimulation energy of a level lower than the level of the stimulation energy of the stimulating rays used in the final read-out, and detecting the light emitted by the stimulable phosphor sheet during the scanning by a photoelectric read-out means.
In order to conduct the preliminary read-out, a read-out section for the preliminary read-out may be provided independently of the read-out section for the final read-out. However, in this case, since two laser beam sources and two photoelectric read-out means are necessary, the manufacturing cost of the apparatus becomes high. In order to eliminate this problem, there has heretofore been used a read-out method wherein the preliminary read-out is conducted by conveying a stimulable phosphor sheet by use of a conveyance means and scanning the overall surface of the stimulable phosphor sheet with stimulating rays at a read-out section for the final read-out, then the conveyance means is switched back to return the stimulable phosphor sheet up to the scanning start position, and the final read-out is conducted by conveying the stimulable phosphor sheet in the same direction as when the preliminary read-out was conducted. However, in the case where the image read-out is carried out in this manner, since the stimulable phosphor sheet conveyed for conducting the preliminary read-out must be switched back and returned to the scanning start position, the length of the read-out section in the sheet conveyance direction must be at least equal to the total length of two stimulable phosphor sheets (i.e. the length of one stimulable phosphor sheet before the scanning position of stimulating rays plus the length of one stimulable phosphor sheet after the scanning position thereof). Thus the read-out section becomes large. Accordingly, in the case where the read-out apparatus is designed so that the preliminary read-out may be conducted, since the read-out section becomes large and consequently the read-out apparatus becomes large as a whole, it is not always possible to substantially satisfy the requirement of minimizing the size of the read-out apparatus.